Polysiloxane compounds, such as dimethylsilicone compounds as typical examples, have conventionally been widely used industrially by themselves or as modifiers for other materials utilizing specific functions such as heat resistance, electrical insulation, flexibility, lubrication and water repellency. For example, polydimethylsiloxane with methacrylic groups at both ends, which is a polymerizable polysiloxane, has been used as a polymer modifier for acrylic polymers or polystyrene, utilizing the polymerization function. Polysiloxanes are used as gas permselective membranes due to high gas permeability and also as biomaterials or medical materials due to little influence on a human body. There are many studies and patent applications on an application to a contact lens utilizing their superior oxygen permeability, flexibility and optical transparency (for example, JP-B-63-29741 and JP Nos. 1430546, 2532406 and 2716181).
Contact lenses are fundamentally classified into a soft and a hard types. Hard contact lenses are literally hard and show an discomfort in wearing. However, a recent remarkable improvement in oxygen permeability has produced products for a continuous wearing. On the other hand, soft contact lenses have features in softness and comfortable in wearing but still have many problems. Soft contact lenses are classified, in detail, to a hydrogel and a non-hydrofel types.
Hydrogel soft contact lenses are composed of copolymers of hydrophilic monomers such as hydroxyethyl methacrylate and N-vinylpyrrolidone as a main component and prepared by lathe-cutting, molding or cast molding methods, followed by a swelling treatment in a physiological saline solution to obtain a lens with water content of about 40-80%.
Non-hydrogel soft contact lenses include, for example, a silicone rubber lens obtained by thermal curing of a mixture of polydimethylsiloxane capped with vinyldimethylsilyl groups at both ends of its molecular chain and methylhydrogenpolysiloxane by molding method after an addition of a platinum-based catalyst, and a flexible lens with an elastic modulus between soft and hard types, composed of polyperfluoroether as a main component, linked with polymerizable groups such as methacrylic groups at both ends (JP Nos. 1278540 and 1677573). Another example for manufacturing a non-hydrogel soft contact lens with comfortable in wearing is preparing a lens by lathe-cutting a hard substrate obtained by a copolymerization of (meth)acrylic acid and (meth)acrylate followed by an esterification and/or a transesterification treatment (JP No. 952157).
There are many inconveniences in handling a hydrous soft contact lens such as poor oxygen permeability, liability to fracture, inferior durability and periodical boiling sterilization required due to an easy deposition of tear components and a possibility of germ growth. Soft contact lens of a higher water content has improved oxygen permeability to a certain extent but is not sufficient enough, and does not have a satisfactory strength for a extended-wearable lens.
On the other hand, a non-hydrogel soft contact lens also has the following problems. Silicone lens, started with a big expectation due to extremely high oxygen permeability, has poor wettability to tear owing to a hydrophobic lens surface. Although surface treatments to improve hydrophilic property such as plasma processing and grafting hydrophilic monomers have been tried but sufficient levels of hydrophilic property and durability have not been obtained. Another problem is an adhesion during wearing and deposition with proteins and lipids in tear. In order to overcome these problems, a hydrogel soft contact lens consisting of silicone hydrogel with high oxygen permeability has been proposed, but it is still insufficient in surface wettability, liable to lipid staining and thus inferior as an extended-wearable lens (for example, Japanese Patent No. 1421481, JP-A-6-503276, JP-A-7-505169, JP-A-7-508063 and JP-A-8-245737).